Telescopic, single-acting hydraulic cylinders can be considered as push actuators. There is a practical limit in increasing the number of telescopic sections of such a hydraulic cylinder for the same to be confined within a minimum longitudinal extent when in retracted position. Therefore, such actuators, depending on the required stroke, occupy quite an important minimum length, when retracted. When used as a lifting device, for instance when several such cylinders are used to lift a floor section of a theatre scene, it is necessary to make important excavations in the ground to house such cylinders at their lower end portion.
It has been found that in certain locations, the water level in the ground does not permit such excavations. Therefore, there is a need for such particular theatre applications and also for some other applications where the available room is limited, to provide a push actuator which takes a minimum of length when retracted relative to its extension stroke.